This invention relates to transparencies to be imaged by a xerographic process, more particularly, to transparencies to be imaged in plain paper-type copiers.
In a "plain paper-type" copier, a copy of an original can be made by the xerographic process on a paper copy sheet of rectangular configuration, which has no special coating. The xerographic process includes the steps of transferring a toner image, formed by conventional means on a photoconductive surface of the copier, to the copy sheet, then fixing the image by fusion of the toner thereto. The fusion most frequently is accomplished by the application of heat to the surface of the copy sheet.
A plain paper copier can be used to copy images from an original onto a transparent copy sheet, of like configuration to the paper sheets and typically made from a thin film of an organic resin, such as a polyester resin. The transparent copy sheets, or "transparencies," as they are commonly known, which are intended for being imaged in plain paper copiers are especially adapted for this use, since the transparent base sheets have neither the same surface, nor the same bulk characteristics as have the opaque cellulosic paper copy sheets for which plain paper copiers originally were designed. For example, a transparent base sheet may be coated, to provide a surface adapted for adheringly receiving, and for having fused thereon, the toner image. The imaged transparency advantageously is used for projecting the image onto a suitable surface, for viewing purposes.
The transparent nature of the transparencies presents a problem, however, in that the transparencies may not be usable in p1ain paper copiers of the kind which employ opacity sensors to detect the presence of copy sheets in the external feed to the copier and/or in the path followed by a copy sheet as it moves through the copier. These sensors are activated by, or respond to, the presence of opacity in the path of a beam of light, visible or infrared, emitted by a suitable source for impinging upon the sensor. In such copiers, if no opacity is present on a copy sheet, the copier will not operate to image the copy sheet.
Transparencies are commercially available for use with certain plain paper copiers having opacity sensors. These transparencies make use of the fact that the opacity sensors of the copiers are positioned therein to respond to a relatively narrow opaque area, which is proximate to an outer edge of a copy sheet. The transparencies are provided with an opaque stripe running along one edge of the sheet, which stripe serves to activate an edge-reading opacity-sensor.
The disposition of edge-reading opacity sensors in plain paper copiers, and the operational requirements of such copiers, are not standardized. The requirements as to whether a stripe must be provided on a longer or on a shorter edge of an elongate rectangular transparency vary with the particular make and/or model of copier. Similarly, the specific orientation of a striped transparency with respect to the copy sheet feed input, and/or to the direction of movement of the copy sheet through the copier, is dependent upon the requirements of the manufacturer of the copier. For example, some copiers require that the striped edge be the leading edge of the copy sheet, i.e., the edge first to enter the copier, and that this edge be perpendicular to the direction of copy sheet movement. Other copiers call for the striped edge to be parallel to the direction of copy sheet movement.
It may occur that an office will have a diversity of plain paper copiers, each perhaps with a different type of copy sheet sensor. Further, the copiers with edge-reading opacity sensors each may have distinctive requirements as to the location of the stripe on a transparency adapted for use with the copier. Consequently, to be able to utilize the maximum number of copiers in an office for making imaged transparencies, several different types of striped transparencies may have to be stocked. Similarly, distributors are required to stock the several types of transparencies. It would be desirable to minimize the number of transparency types that must be stocked.
Also, the requirements of the copier in regard to the orientation of the sheet relative to the copier must be observed by the operator. Increased time taken by an operator to ensure proper orientation increases the overall cost of making an imaged transparency. It would be desirable also to provide a transparency requiring relatively little care and expenditure of time in feeding the transparency to a copier.